Group Number

This is a bit of a controversial topic. There are many differing opinions on the proper number of people in a group for optimized survival chances. Some people believe that getting a large group together is best. Some think a person should go it alone, maybe with a dog. I, on the other hand, believe in a small group. Ideally four or five. Seven is the max number of people that should be in your group. After seven it becomes hard to keep track of everybody. When you lose track of people you have an increased chance of a member of your party becoming infected without anyone noticing. 

If you know a Navy Seal, he is the leader. Don't argue it.

An important part of surviving as a group in the Zombie Invasion is decisiveness. Democratic systems are all well and good, but when decisions need to be made in emergency situations someone needs to step up and make those decisions. Nothing will get your group killed faster than standing around debating options. To that end a leader MUST be selected. His orders, in survival situations, are to be followed. The leader has to be someone that everyone trusts to work in the entire group's best interest.

This, in my opinion, is the system that will give you the best chance for survival.